Laser Surgery for Glaucoma
Chat Highlights
May 7, 2008

On Wednesday, May 7, 2008, 2008, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Laser Surgery for Glaucoma".

Moderator: Welcome back to chat Dr. Pro. Thank you for joining us. Tonight our topic is “Laser Surgery for Glaucoma.” First, could you tell us how many different types of lasers are used in glaucoma and then we will examine each type in more detail?

Dr. Pro:  There are different lasers for different types of glaucoma: Argon lasers, "YAG" lasers, Diode lasers. SLT. There are many types. Perhaps it is better to address the type of glaucoma to be treated and talk of the kind of laser that is used.

Moderator: Shall we start with angle closure?

Dr. Pro:  OK, for that the Nd:YAG is used to perform a Laser Iridotomy. This is a treatment for angle closure glaucoma, prophylactic for patients with narrow angles and is also used sometimes for pigment dispersion syndrome. Laser Iridotomy opens the angle to help prevent chronic angle closure glaucoma and acute angle closure attacks.

Moderator: What do the initials Nd:YAG stand for?

Dr. Pro:  Nd: YAG = Neodimium Doped Yttrium Aluminum Garnet. This is the crystal used in the laser. [see Wikipedia http://en.wikipedia.org/wiki/Nd:YAG_laser – ed]

A laser is a device that creates and amplifies a narrow, intense beam of coherent light; atoms of a crystal or molecule are excited so that they give off energy in the same direction, hitting a photon and a burst of light of a single wavelength is produced.

P:  Why are some green and some red? Are they different intensities for the laser beam?

Dr. Pro:  The color depends on the wavelength of the excited light, which depends on the crystals used.

Moderator: Thank you doctor. Shall we continue to lasers for open angle?

Dr. Pro:  Different lasers are used for open angles. For open angle glaucoma and ocular hypertension, lasers are often an adjunct to drops. Sometimes laser surgery may be able to replace drops, and/or may delay need for incisional surgery.

Selective Laser Trabeculoplasty (SLT, a type of YAG laser) and Argon Laser Trabeculoplasty (ALT) show similar long-term success rates. SLT selectively targets pigmented cells and delivers less than 1% of the energy of ALT, and is repeatable.

The average IOP reduction is usually about 20% at one to two years (This is an average of many studies).

P:  How is it determined whether ALT or SLT is used? Can a patient have both?

Dr. Pro:  The laser used somewhat depends on what the physician has in the office.
I want to stress that both are equally effective as proven in many articles, but the ALT was first, and it does cause permanent coagulative changes in the trabecular meshwork (the drain of the eye located between the iris and the cornea). The SLT causes no discernable changes to the trabecular meshwork and can be repeated.

P:  During both an ALT & SLT, I have heard a Rice Krispies "snap, crackle, pop" sound in my eye. What is crackling?

Dr. Pro:  The lasers cause small bubbles to form in the eye. Maybe you heard them, but I never had a patient report that yet.

P:  Can the ALT be repeated at all?

Dr. Pro:  Yes, there are some studies that have demonstrated that it can, but it can also cause the pressure to go up because of the formation of permanent scar tissue in the drain.

P:  Does the laser's success depend upon the amount of pigment?

Dr. Pro:  Yes, it seems to, although the data on that point is not too clear. I have certainly seen that in my patients; there may even be a racial difference.

In the Advanced Glaucoma Intervention Study (AGIS) black patients had a lower risk of failure with ALT than whites (36% with visual field worsening for blacks versus 40% with visual field worsening for whites)

P:  It looks and sounds like those data mean if I get SLT I have a 40% chance of walking out worse than when I went in. That cannot be what was meant.

Dr. Pro:  I did not say that. The data comes from a study of patients with advanced glaucoma, where specific treatment protocols were used to keep the IOP down. In some patients the glaucoma progressed in spite of treatment, but would likely have been worse were there no treatment given.

Moderator: Are there any other types of glaucoma and lasers to touch on?

Dr. Pro:  Sure, for a minute let's go back to narrow angles and angle closure. I should add that an iridotomy is usually the first treatment in an angle closure attack, but the YAG is not the only laser used.

In the past we only had the argon which can also be used to make a PI (peripheral iridotomy), but there is now another narrow angle or angle closure laser procedure available called Iridoplasty. This is used with plateau iris configuration or acute angle closure with a cloudy cornea, through which making a PI would be impossible. The laser Iridoplasty creates peripherally placed argon contraction burns which physically pull the iris out of the angle and can break an angle closure attack or help open the angle for chronic conditions.

P:  Do these surgeries require great skill so that years of experience would be beneficial? In other words, would a doctor with many of these under his belt be better than a lesser-experienced doctor?

Dr. Pro:  These procedures are really technically pretty easy. Most doctors can get similar results.

P:  My doctor did SLT in both eyes three and a half years ago and said we could repeat it in maybe three years, then he retired. My pressures are creeping right back up, but my new doctor doesn't seem to want to repeat the SLT because I would have to pay for it. That's ok with me! What should I say?

Dr. Pro:  Well, I guess it depends on what other therapies have been attempted. If drops are not working and there is worry that the glaucoma could progress it makes sense to try an SLT. Remember the success is not guaranteed, but the downsides are usually minimal for an SLT.

P:  Is laser recommended for advanced POAG patients?

Dr. Pro:  I feel that laser in advanced POAG patients is usually not enough. Remember, that the IOP reduction is about 20%. I don't mean to be pessimistic, but the long-term success (three to five years) is a bit over 30%, so I think advanced POAG patients may benefit from incisional surgery if the glaucoma is progressing.

P:  I believe the risk of SLT laser trabeculoplasty and laser for posterior lens capsule is low. Do you know the percentage risk, for example, a one percent risk?

Dr. Pro:  I don't know that percentage, but the risk is very, very small.

P:  Does having a lens implanted in front of the iris frequently cause a closed angle situation? I had an iridectomy when a lens was put in front of my iris. Does the drain go all the way around the outside of the iris, or is the drain just in one spot on the outer edge of the iris?

Dr. Pro:  When a lens is in front of the iris, the iris can drape around the lens and access to the drain is blocked. The PI allows the fluid to get into the anterior chamber and through the drain.

P:  What are the risks associated with an ALT or SLT? Can the SLT worsen a patient's vision?

Dr. Pro:  They may cause transient blurred vision, a post-laser pressure spike, or post-laser inflammation. The SLT usually does not affect the vision beyond several days after the procedure.

P:  After two SLT's that did not lower my pressure at all, my doctor wants to do a third within an 18-month time frame to keep my pressure from rising above its current 22. Can a SLT keep eye pressure from increasing?

Dr. Pro:  It does seem that your track record for success with the SLT is low. Although I can't predict, there are individuals who do not respond to SLT (I think in my practice about 20% have no response).

P:  Where is the drain?

Dr. Pro:  Between the cornea and the iris in the angle of the eye.

P:  Why do lasers have better results on those over 60 years of age?

Dr. Pro:  That data comes from the ALT studies, I don't know if it is true for the SLT as well. I certainly don't use an SLT in children, but have had success in young adults. We don't know why the ALT or maybe SLT doesn't work as well in young people.

P:  Do you have an opinion on ALPI - iridoplasty? Is it successful and can it be repeated?

Dr. Pro:  It is most successful in plateau iris configuration, which is a specific configuration of how the iris inserts into the angle. It can be repeated, but it does cause distortion of the pupil if done too much.

P:  What eye drops are administered prior to either laser procedure and what is their purpose?

Dr. Pro:  Usually we give either Iopidine or Alphagan. Sometimes pilocarpine for a PI or SLT/ALT. to bring the pupil down.

P:  What is the risk from incisional surgery after SLT has been tried? Fear of a bad result is my biggest reluctance; but maybe I shouldn't be so afraid.

Dr. Pro:  That is the topic for a whole chat. Any incisional surgery carries the risk of infection, bleeding, or blindness, which is low. Bleb complications include late infection, bleb leak, etc. But it can be the best way to control the IOP and arrest glaucoma progression.

P:  I had three SLT's with no result (one in each half of L eye and another in half of the R eye). Is there anything I can surmise from this about my eyes?

Dr. Pro:  SLT may not work for you. But drops may be effective.

P:  Can a patient drive after either laser procedure or do they need to arrange a ride?

Dr. Pro:  They can usually drive, but I tell my patients that the vision in the eye may be a bit blurry that day (kind of like when you are dilated). I ask them to be driven or take a bus if they have any worries.

P:  What is the difference between iridotomy and iridectomy?

Dr. Pro:  Iridotomy is from a laser, iridectomy is a surgical procedure. Before the argon, this was made in the operating room.

Dr. Pro:  I want to mention another type of laser. The SLT, ALT, PI all help the fluid drainage from the eye. There is a means to turn down the fluid production in the eye and is becoming more popular.

Endocyclophotcoagulation is a cyclodestructive procedure used on pseudophakic eyes (eyes with an IntraOcular Lens—IOL—implant). It is often used during cataract surgery on patients on one or two medications. It has the advantage of direct visualization of ciliary body on video monitor with low energy laser emissions.

There are always new lasers in development, but we are lucky to have the range of options today that did not exist even 10 years ago. Good night, everyone.

Moderator: Good Night Dr Pro. Thank you; see you soon!

Dr. Pro:  You are welcome, bye.

On May 21, Dr. Pro discussed "Glaucoma Medications" in the Chat room. Click here for highlights of that meeting.

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